My dictionary gives as definition of a separate word, the Latin "pace", the ablative of "oax".
It is used to indicate polite disagreement, as in:
"A good example of this process is the widespread adoption of---pace the House
of Lords--- "gay" usage." (in reference to previously mentioned complaint by a member of the
House of Lords that poets could no longer use the word "gay" in its old sense)

My dictionary says that "pace" is a preposition. Please, someone whose command of grammar
is greater than mine, explain how it is a preposition.